Many people are getting their hands on Google Analytics 4 aka GA4 and they need to understand:

1. Session Source/Medium Dimension: For sessions lacking the automatically captured session_start event, the report will show “not set” under the session source/medium.

2. Landing Page Dimension: The term “not set” may appear under the landing page dimension if a session doesn’t include a page_view event.

3. Content Group Dimension:

When pairing the content group dimension with automatically collected events like session_start or first_visit, “not set” may appear. This discrepancy arises because these automatically captured events don’t recognize the content_group parameter, making the data combination invalid.
Additionally, “not set” will display if an event transmits the content_group parameter with an empty value, e.g., (content_group: “”).

4. Auto-Tagging Status: Ensure auto-tagging is activated. If not, familiarize yourself with the steps to enable it. (regarding Google Ads). Do not use UTM’s and Auto Tagging with Google Ads, if you do not know what are the consequences because data will be mismatched

5. Traffic from Unlinked Google Ads Accounts: Should the GCLID parameter persist on your Google Ads final URLs, verify if there are other Google Ads accounts promoting your website that haven’t been linked to your GA4 account. Traffic from these unlinked accounts will be denoted as “not set” in Google Ads reports, given the inability to associate these conversion events with a specific click.

6. Manually Tagged Destination URLs: When using manual tagging of destination URLs with UTM parameters instead of auto-tagging, “not set” may appear for URLs with incorrect or missing parameters. Such URLs could originate from Google Ads accounts and other platforms like social networks, blogs, or distinct websites. In cases where Analytics fails to get the required parameters to determine the origin of traffic from manually tagged URLs, it defaults to “not set”.

7. Consent Mode V2 not correctly configured: When using a consent banner solution you should take care if the right signals are sent when the user consents or does not consent (see article about consent mode v2)

If you’re experiencing challenges with your data analytics, we offer a complimentary Quick Audit to assess the status of your Google Analytics 4 migration. Visit our website at https://ittechbuz.com/quick-audit-google-analytics-4 to learn more.

reference:

https://support.google.com/analytics/answer/13504892